PANCREASPANCREAS

ObjectivesObjectives

The students should be able to describe:The students should be able to describe:

1.1.The The endocrine partendocrine part of the pancreas of the pancreas within the exocrine portion.within the exocrine portion.

2.2.The The histological featureshistological features of the cells of of the cells of Islet of Langerhans.Islet of Langerhans.

3.3.The The functionfunction of different cells of Islets of of different cells of Islets of Langerhans.Langerhans.

PANCREASPANCREAS

Stroma:Stroma: capsule, capsule, septa & reticular fibers.septa & reticular fibers.

Parenchyma:Parenchyma: Pancreas is a Pancreas is a mixedmixed gland:gland:– Exocrine part Exocrine part (acini & (acini &

ducts): produces ducts): produces digestive pancreatic digestive pancreatic enzymesenzymes..

– Endocrine part Endocrine part (islets (islets of Langerhans): of Langerhans): produces produces hormoneshormones..

Exocrine PancreasExocrine Pancreas

Pancreatic Acini:Pancreatic Acini: Serous acini with:Serous acini with:

– Centroacinar cells (the Centroacinar cells (the beginning of the ducts).beginning of the ducts).

– No myoepithelial cells.No myoepithelial cells.

Nuclei are basal.Nuclei are basal. Cytoplasm:Cytoplasm:

– Basal part basophilic (due Basal part basophilic (due to abundant rER).to abundant rER).

– Apical part acidophilic Apical part acidophilic (due to secretory (due to secretory granules).granules).

Exocrine PancreasExocrine Pancreas

Duct System:Duct System: CentroacinarCentroacinar cells. cells. IntercalatedIntercalated ducts (low ducts (low

cuboidal).cuboidal). IntralobularIntralobular ducts (NOT ducts (NOT

prominent).prominent). InterlobularInterlobular ducts. ducts. MainMain pancreatic duct. pancreatic duct.

Endocrine PancreasEndocrine Pancreas

Islets of Langerhans:Islets of Langerhans: Pale-staining spherical Pale-staining spherical

collections of endocrine cells, collections of endocrine cells, scattered among the acini.scattered among the acini.

Richly vascularized by Richly vascularized by fenestrated capillaries.fenestrated capillaries.

Each islet is surrounded and Each islet is surrounded and supported by reticular fibers.supported by reticular fibers.

1 million islets in human 1 million islets in human pancreas.pancreas.

Most numerous in the tail of Most numerous in the tail of pancreas.pancreas.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: 5 types of cells in each islet:5 types of cells in each islet:

1.1. ββ (B) cells: (B) cells: secrete insulin.secrete insulin.

2.2. αα (A) cells: (A) cells: secrete glucagon.secrete glucagon.

3.3. δδ (D) cells: (D) cells: secrete secrete somatostatin.somatostatin.

4.4. G cells: G cells: secrete gastrin.secrete gastrin.

5.5. PP cells: PP cells: secrete pancreatic secrete pancreatic polypeptide.polypeptide.

Cannot be differentiated from Cannot be differentiated from one another by routine stains.one another by routine stains.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: ββ (B) cells: (B) cells:

– Constitute 70% of islet cells.Constitute 70% of islet cells.– Concentrated in islet center.Concentrated in islet center.– Function: secrete Function: secrete insulininsulin which which

↓ blood sugar.↓ blood sugar.

αα (A) cells: (A) cells:– Constitute 15-20%.Constitute 15-20%.– Concentrated in islet periphery.Concentrated in islet periphery.– Granules are much more Granules are much more

numerous, more tightly numerous, more tightly packed, smaller, and denser packed, smaller, and denser than those of β cells.than those of β cells.

– Function: secrete Function: secrete glucagonglucagon which ↑ blood sugar.which ↑ blood sugar.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: δ (δ (D) cells:D) cells:

– Constitute 5-10% of islet Constitute 5-10% of islet cells.cells.

– Scattered throughout the Scattered throughout the islet.islet.

– Granules are less dense Granules are less dense than those of β and than those of β and α α cells.cells.

– Function: secrete Function: secrete somatostatinsomatostatin which ↓ release which ↓ release of hormones from endocrine of hormones from endocrine pancreas and enzymes from pancreas and enzymes from exocrine pancreas.exocrine pancreas.

Endocrine PancreasEndocrine Pancreas

Cells of the Islets:Cells of the Islets: G cells:G cells:

– Constitute 1% of islet cells.Constitute 1% of islet cells.– Scattered throughout the islet.Scattered throughout the islet.– Function: secrete Function: secrete gastringastrin which ↑ production of HCl which ↑ production of HCl

by parietal cells of stomach.by parietal cells of stomach.

PP cells:PP cells:– Constitute 1% of islet cells.Constitute 1% of islet cells.– Scattered throughout the islet.Scattered throughout the islet.– Function: secrete Function: secrete pancreatic polypeptidepancreatic polypeptide which ↓ which ↓

exocrine secretions of pancreas.exocrine secretions of pancreas.

Clinical CorrelationsClinical Correlations

Diabetes mellitus:Diabetes mellitus: A hyperglycemic metabolic disorder that results A hyperglycemic metabolic disorder that results

from:from:(1)(1) lack of insulin production by β cells of the islets of lack of insulin production by β cells of the islets of

Langerhans, orLangerhans, or

(2)(2) defective insulin receptors on the target cells.defective insulin receptors on the target cells.

There are two major forms of diabetes mellitus, There are two major forms of diabetes mellitus, type 1 and type 2. Type 2 is more common.type 1 and type 2. Type 2 is more common.

The most significant laboratory result indicative of The most significant laboratory result indicative of diabetes is elevated blood diabetes is elevated blood glucose glucose levels after an levels after an overnight fast.overnight fast.

Best wishes

Best wishes